1. Field of the Invention
This invention relates to a process for the production of a stabilized polycarbonate. More specifically, this invention relates to a process for the production of a stabilized polycarbonate excellent in melt stability, melt moldability, resistance to hydrolysis and hue.
2. Description of Related Art
Polycarbonates are excellent in mechanical properties such as impact strength, etc. and in transparency, and find application in various fields. As a process for producing polycarbonates, there have been known an interfacial process in which a dihydroxy compound and phosgene are directly reacted and a melting process in which a dihydroxy compound and a carbonic acid diester are subjected to an ester interchange reaction under reduced pressure with heating.
The latter melting process is preferable to the former interfacial process because a polycarbonate resin can be produced advantageously at low cost and without using a solvent such as methylene chloride or the like which is desirable from the environmental aspect.
In a conventional process for producing a polycarbonate by melting, an alkali metal compound or an alkaline earth metal compound is usually used as a catalyst component. A polycarbonate resin obtained by using such a catalyst, however, involves problems that it lacks a melt stability due to the incorporated catalyst, and that in melt-molding, part of the polycarbonate resin is sometimes thermally decomposed, its molecular weight is decreased, its transparency is decreased, the polycarbonate resin is colored, and so forth.
Japanese Patent Publication No. 44,303/1979 discloses a method for stabilizing a polycarbonate resin in which methyl benzenesulfonate or a compound represented by the formula ##STR1## wherein R.sub.1 is a C.sub.1-12 alkyl group, and R.sub.2 is a C.sub.1-6 alkyl group, is added
to a polycarbonate resin. The polycarbonate resin obtained by this method, however, tends to yellow in melt-molding and is still insufficient in resistance to hydrolysis. Accordingly, it is demanded to develop a polymerization catalyst and additives or a polymerization technique to solve such problems.
Japanese Laid-open Patent Application No. 171,024/1993 (Kokai Sho 64-13267) discloses a polycarbonate resin composition comprising 100 parts by weight of a polycarbonate resin, 0.1 to 20 parts by weight of a sulfonic acid phosphonium salt represented by the formula ##STR2## wherein R.sup.1 is a C.sub.1-40 alkyl group or an aryl group, and each of R.sup.2 to R.sup.5 is independently H, a C.sub.1-10 alkyl group or an aryl group,
and 0.01 to 3.0 parts by weight of a sulfur-containing ester compound.
Japanese Laid-open Patent Application (Kokai) No. 14,267/1989 discloses a polycarbonate resin composition corresponding to the above composition in which the sulfur-containing ester compound is replaced with a phosphite ester.
The above two polycarbonate resin compositions containing the sulfonic acid phosphonium salt are both to impart an antistatic property, and for this purpose the sulfonic acid phosphonium salt has to be used in an amount as large as 0.1 to 20 parts by weight per 100 parts by weight of the polycarbonate resin. Therefore, this polycarbonate resin involves a problem that there occur results which are not necessarily desirable for important basic properties of the polycarbonate resin, such as a hue and a resistance to hydrolysis.
Japanese Laid-open Patent Application No. 9,285/1993 (Kokai Hei 5-9285) discloses a process for producing a polycarbonate, which comprises adding 0.05 to 10 ppm of a sulfonic acid compound represented by the formula ##STR3## wherein R.sup.7 is a C.sub.1-6 hydrocarbon group which may be substituted with halogen, R.sup.8 is H or a C.sub.1-8 hydrocarbon group which may be substituted with halogen, and n is an integer of 0 to 3,
to a polycarbonate obtained by melt polycondensation of an aromatic dihydroxy compound and a carbonic acid diester. This document simply describes a compound having a primary alkyl group as a compound in which the C.sub.1-8 hydrocarbon group is an alkyl group.
British Patent No. 808,488 specification discloses a process for the production of high-molecular-weight fiber and film forming polycarbonates by interesterification or polycondensation in the presence of basic catalysts which comprises neutralizing the catalysts in the course of or at the end of the interesterification or polycondensation respectively by adding base-binding materials to the melt. Dialkyl sulphates such as dimethyl sulphate and dibutyl sulphate are shown as the base-binding materials.
British Patent No. 808,489 specification discloses also a process for the production of high-molecular-weight polycarbonates by interesterification. Towards the end of the interesterification, basic catalysts are neutralized with base-binding materials, especially volatile base-binding materials such as dimethyl sulphate.
Japanese Laid-open Patent Application No. 17,564/1993 (Kokai Hei 5-17564) discloses a process for producing a polycarbonate, which comprises melt-polycondensing an aromatic dihydroxy compound and a carbonic acid diester in the presence of a catalyst formed of a nitrogen-containing basic compound (1st step), and then adding a nitrogen-containing basic compound at least once and further a sulfonic acid compound represented by the formula ##STR4## wherein R.sup.31 is a C.sub.1-6 hydrocarbon group which may be substituted with halogen, R.sup.32 is H or a hydrocarbon group which may be substituted with halogen, and n is an integer of 0 to 3,
in an amount of 0.05 to 10 ppm of a polycarbonate to be obtained in subsequent polymerization steps.
It is an object of this invention to provide a process for the production of a stabilized polycarbonate.
Another object of this invention is to provide a process for the production of a polycarbonate excellent in melt stability, resistance to hydrolysis, melt moldability and hue.
The other objects and advantages of this invention will be made clear from the following explanation.